Characterization of a major late herpes simplex virus type 1 mRNA

Lytic HSV-1 infection induces the multifunctional transcription factor Early Growth Response-1 (EGR-1) in rabbit corneal cells

BACKGROUND

Herpes simplex virus type-1 (HSV-1) infections can cause a number of diseases ranging from simple cold sores to dangerous keratitis and lethal encephalitis. The interaction between virus and host cells, critical for viral replication, is being extensively investigated by many laboratories. In this study, we tested the hypothesis that HSV-1 lytic infection triggers the expression of important multi-functional transcription factor Egr1. The mechanisms of induction are mediated, at least in part, by signaling pathways such as NFκB and CREB.

METHODS

SIRC, VERO, and 293HEK cell lines were infected with HSV-1, and the Egr-1 transcript and protein were detected by RT-PCR and Western blot, respectively. The localization and expression profile of Egr-1 were investigated further by immunofluorescence microscopy analyses. The recruitment of transcription factors to the Egr-1 promoter during infection was studied by chromatin immunoprecipitation (ChIP). Various inhibitors and dominant-negative mutant were used to assess the mechanisms of Egr-1 induction and their effects were addressed by immunofluorescence microscopy.

RESULTS

Western blot analyses showed that Egr-1 was absent in uninfected cells; however, the protein was detected 24-72 hours post treatment, and the response was directly proportional to the titer of the virus used for infection. Using recombinant HSV-1 expressing EGFP, Egr-1 was detected only in the infected cells. ChIP assays demonstrated that NFкB and cAMP response element binding protein (CREB) were recruited to the Egr-1 promoter upon infection. Additional studies showed that inhibitors of NFкB and dominant-negative CREB repressed the Egr-1 induction by HSV-1 infection.

CONCLUSION

Collectively, these results demonstrate that Egr-1 is expressed rapidly upon HSV-1 infection and that this novel induction could be due to the NFкB/CREB-mediated transactivation. Egr-1 induction might play a key role in the viral gene expression, replication, inflammation, and the disease progression.

Identification of a novel expressed open reading frame situated between genes U(L)20 and U(L)21 of the herpes simplex virus 1 genome

An open reading frame (ORF) situated between the U(L)20 and U(L)21 genes encodes a protein designated as U(L)20.5. The U(L)20.5 ORF lies 5' and in the same orientation as the U(L)20 ORF. The expression of the U(L)20.5 ORF was verified by RNase protection assays and by in-frame insertion of an amino acid sequence encoding an epitope of an available monoclonal antibody. The tagged U(L)20.5 protein colocalized in small dense nuclear structures with products of the alpha22/U(S)1.5, U(L)3, and U(L)4 genes. Expression of the U(L)20.5 gene was blocked in cells infected and maintained in the presence of phosphonoacetate, indicating that it belongs to the late, or gamma(2), kinetic class. U(L)20.5 is not essential for viral replication inasmuch as a recombinant virus made by insertion of the thymidine kinase gene into the U(L)20.5 ORF replicates in all cell lines tested [J. D. Baines, P. L. Ward, G. Campadelli-Fiume, and B. Roizman (1991) J. Virol. 65, 6414-6424]. The genomic location of the recently discovered genes illustrates the compact nature of the viral genome.

The UL10 gene of herpes simplex virus 1 encodes a novel viral glycoprotein, gM, which is present in the virion and in the plasma membrane of infected cells

The herpes simplex virus 1 UL10 gene encodes a hydrophobic membrane protein dispensable for viral replication in cell culture (J.D. Baines and B. Roizman, J. Virol. 65:938-944, 1991). We report the following. (i) A fusion protein consisting of glutathione S-transferase fused to the C-terminal 93 amino acids of the UL10 protein was used to produce a rabbit polyclonal antiserum. The antiserum reacted with infected-cell proteins which formed in denaturing polyacrylamide gels a sharp band (apparent M(r) of 50,000) and a very broad band (M(r) of 53,000 to 63,000). These bands were not formed by lysates of UL10- virus or by lysates of infected cells boiled in the presence of sodium dodecyl sulfate before electrophoresis. (ii) The proteins forming both bands were labeled by [3H]glucosamine, indicating that they were glycosylated. (iii) The UL10 protein in cells treated with tunicamycin formed a single band (apparent M(r) of 47,000) reactive with the anti-UL10 antibody, indicating that the 47,000-M(r) protein was a precursor of N-glycosylated, more slowly migrating forms of UL10. Treatment of the immunoprecipitate with endoglycosidase H increased the electrophoretic mobility of the 50,000-M(r) species to that of the 47,000-M(r) species, indicating that the 50,000-M(r) species contained high-mannose polysaccharide chains, whereas the proteins forming the 53,000- to 63,000-M(r) bands contained mature chains inasmuch as they were resistant to digestion by the enzyme. (iv) The UL10 protein of R7221 carrying a 20-amino-acid epitope formed only one band with an M(r) of 53,000. This band was sensitive to endoglycosidase H, suggesting that the epitope inserted in the R7221 UL10 protein may have interfered with glycosylation. (v) The UL10 protein does not contain a cleavable signal sequence inasmuch as the first UL10 methionine codon was reflected in the 50,000-M(r) protein. (vi) The UL10 protein is present in virions and plasma membranes of unfixed cells that were reacted with the polyclonal rabbit antibody. In accordance with the current nomenclature, the UL10 protein is designated glycoprotein M.

Herpes simplex virus type 1 mutant strain in1814 establishes a unique, slowly progressing infection in SCID mice

Ocular infection of immunocompetent (BALB/c) mice with wild-type herpes simplex virus type 1 (HSV-1) 17+ may lead to acute fatal encephalitis; however, in surviving animals, a latent (nonproductive) infection of the nervous system is established. In contrast, 17+ infection invariably kills mice with severe combined immunodeficiency (SCID mice) within 2 weeks. Ocular infection of immunocompetent mice with a mutant HSV-1 strain, in1814, which does not produce a functional alpha-transinducing protein, results in no detectable viral replication in the nervous system during the time corresponding to the acute phase of infection, no mortality, and the establishment of latency. In SCID mice, however, the in1814 virus establishes a unique, slowly progressing infection. In studying the courses of in1814 infection in SCID and BALB/c mice, we found that although intact B- and/or T-lymphocytic functions were required for the control of viral replication in the nervous system, some of the infected neurons of SCID mice seemed to be able to restrict in1814 replication and harbor the virus in a latent state.

Induction of cellular transcription factors in trigeminal ganglia of mice by corneal scarification, herpes simplex virus type 1 infection, and explantation of trigeminal ganglia

In a mouse model for herpes simplex virus type 1 (HSV-1) latency in which the virus was inoculated via the eye after corneal scarification, HSV-1 replicated in corneal epithelial cells and infected the nerve cell endings. HSV-1 reached the trigeminal ganglia by fast axonal transport between 2 and 10 days postinfection (p.i.) and established a latent infection in neuronal cells or replicated and spread to nonneuronal cells. By using in situ hybridization, we showed that cellular transcription factors are stimulated by HSV-1 infection in trigeminal ganglia. This stimulation is biphasic, peaking at 1 and 3 to 4 days p.i. The first peak involves c-jun and oct-1 expression in neurons, and the second involves c-jun, c-fos, and oct-1 expression in neurons and nonneuronal cells. Corneal scarification, alone or followed by infection with UV-inactivated HSV-1, induced monophasic c-jun and oct-1 expression in some neurons of the trigeminal ganglia, with a peak at 1 day p.i. Corneal infection without prior scarification induced c-jun, c-fos, and oct-1 expression in some neuronal and nonneuronal cells of the trigeminal ganglia 2 to 9 days p.i. Explanation of ganglia from latently infected animals resulted in reactivation of the latent virus. Independently of the presence of latent HSV-1 in explanted ganglia, expression of c-fos, c-jun, and oct-1 was induced first in nonneuronal cells, peaking 6 to 10 h postexplantation, and then in neuronal cells, with a peak at 24 h after explantation when expression of viral replicative genes was first detectable. Since ocular HSV-1 infection, corneal scarification, and explantation of trigeminal ganglia all resulted in induction of expression of cellular transcription factors in ganglia, these factors may play a critical role in the permissiveness of cells for HSV-1 replication during acute infection, latency, and reactivation.

Transcriptional analysis of the eight-kilobase mRNA encoding the major capsid protein of human cytomegalovirus

The 8-kilobase mRNA coding for the major capsid protein (MCP) of human cytomegalovirus was precisely mapped. Two 5' ends of the transcript were located within HindIII fragment a, 29 and 34 base pairs, respectively, downstream of the sequence TATTAGA. The 3' end was localized within HindIII fragment b of the viral genome. The MCP transcript was synthesized at late times after infection and was not detected before viral DNA replication. In addition, the MCP promoter region could be identified, which strongly responded to viral trans activation at early and late times after infection in a transient expression assay.

Latent herpes simplex virus type 1 transcripts in peripheral and central nervous system tissues of mice map to similar regions of the viral genome

Herpes simplex virus type 1 (HSV-1) DNA and RNA have been detected in peripheral nervous system (PNS) and central nervous system (CNS) tissues of latently infected mice. However, explant methods are successful in reactivating HSV-1 only from latently infected PNS tissues. In this report, latent herpesvirus infections in mouse PNS and CNS tissues were compared by in situ hybridization to determine whether the difference in reactivation was at the level of the virus or the host tissue. It was demonstrated that the HSV-1 transcripts present during latency in the mouse PNS and CNS originated from the same region of the genome, the repeats which bracket the long unique sequence. Therefore, the difference in reactivation with PNS and CNS tissues cannot be accounted for by differences in the extent of the HSV-1 genome transcribed during herpesvirus latency. Latent HSV-1 RNA was detected in the trigeminal ganglia (PNS) and the trigeminal system in the CNS from the mesencephalon to the spinal cord as well as other regions of the CNS not noted previously. Latent HSV-1 RNA was found predominantly in neurons but also in a small number of cells which could not be identified as neuronal cells. It is suggested that host differences in CNS and PNS tissues, rather than differences in latent virus transcription, may be important determinants in the HSV-1 reactivation process in explanted tissues.

RNA from an immediate early region of the type 1 herpes simplex virus genome is present in the trigeminal ganglia of latently infected mice

Transcription of the type 1 herpes simplex virus (HSV-1) genome in trigeminal ganglia of latently infected mice was studied using in situ hybridization. Probes representative of each temporal gene class were used to determine the regions of the genome that encode the transcripts present in latently infected cells. Probes encoding HSV-1 sequences of the five immediate early genes and representative early (thymidine kinase), early-late (major capsid protein), and late (glycoprotein C) genes were used in these experiments. Of the probes tested, only those encoding the immediate early gene product infected-cell polypeptide (ICP) 0 hybridized to RNA in latently infected tissues. Probes containing the other immediate early genes (ICP4, ICP22, ICP27, and ICP47) and the representative early, early-late, and late genes did not hybridize. Two probes covering approximately equal to 30% of the HSV-1 genome and encoding over 20 early and late transcripts also did not hybridize to RNA in latently infected tissues. These results, with probes spanning greater than 60% of the HSV-1 genome, suggest that transcription of the HSV-1 genome is restricted to one region in latently infected mouse trigeminal ganglia.

The effect of elevated levels of herpes simplex virus alpha-gene products on the expression of model early and late genes in vivo

The rate of synthesis in vivo and the steady-state level of mRNA of four "model" herpes simplex virus type 1 (HSV-1) genes were measured as a function of high levels of alpha-gene products. The genes studied were ICP4 (alpha), deoxy-UTPase (beta), VP5 (beta gamma), and glycoprotein C (gC, gamma). Accumulation of high levels of alpha proteins was accomplished either by infection with an HSV-1 mutant, temperature-sensitive in ICP4 (ts606) at the nonpermissive temperature then shift-down to permissive temperature, or by infection with wild-type virus under cycloheximide blockage of protein synthesis followed by release. Compared to RNA expression in normal infections, beta gamma and gamma transcription rates were both transiently stimulated under the experimental conditions employed. The greatest effect was seen with the gamma-gC mRNA transcription rates. In addition, at nonpermissive temperatures with ts 606, the amount of expression of gC mRNA was significantly increased over normal early levels, in contrast to the case with the VP5 transcript. The impact of such results on models of HSV gene expression in vivo are discussed.

RNA complementary to a herpesvirus alpha gene mRNA is prominent in latently infected neurons

In initial attempts to define the molecular events responsible for the latent state of herpes simplex virus, in situ hybridization was utilized to search for virally encoded RNA transcripts in latently infected sensory neurons. The use of cloned probes representing the entire viral genome indicated that transcripts encoded within terminal repeats were present. When the alpha genes encoding ICP-0, ICP-4, and ICP-27 and the gamma 1 gene encoding VP-5 were employed, only RNA transcripts hybridizing to the ICP-0 probe were detected. In latently infected cells, the ICP-0--related transcripts were localized principally in the nucleus; this was not the case in acutely (productively) infected neurons or in neurons probed for RNA transcripts coding for actin. In Northern blotting experiments, an RNA of 2.6 kilobases was detected with the ICP-0 probe. When single-stranded DNAs from the ICP-0 region were used as probes, RNA from the strand complementary to that encoding ICP-0 messenger RNA (mRNA) was the major species detected. This RNA species may play a significant role in maintaining the latent infection.

The promoter for the late gene encoding Vp5 of herpes simplex virus type 1 is recognized by cell extracts derived from uninfected cells

The ability of whole-cell extracts from uninfected HeLa cells to recognize the promoter for the herpes simplex virus type 1 late gene encoding the major capsid protein Vp5 was investigated by using both in vitro transcriptional and S1 nuclease protection analysis. This gene promoter was recognized by the cell extracts and produced abundant amounts of transcript in the absence of any other virus-encoded factors. This transcript was shown to arise, in vitro, from specific initiation at or very near the physiological mRNA start site. Thus, it appears that cell extracts from uninfected HeLa cells can efficiently recognize both early- and late-gene promoters.

The properties and sequence of glycoprotein H of herpes simplex virus type 1

The map position of the coding sequence of glycoprotein H of herpes simplex virus type 1 was determined by marker transfer studies in which DNA fragments cloned from a virus resistant to neutralisation by an anti-gH monoclonal antibody were used to transfer antibody resistance to wild type virus DNA following cotransfection. The gH coding sequence was mapped to the BglII "m" fragment of HSV-1 DNA (map coordinates 0.27-0.312), confirming the map position previously determined by intertypic recombinant analysis (Buckmaster et al., 1984). The complete nucleotide sequence of the BglII "m" fragment revealed two large open reading frames in addition to the thymidine kinase gene. The open reading frame lying immediately 3' of the thymidine kinase gene has a predicted translation product with the features of a large glycoprotein. This open reading frame translates to an amino acid sequence of 90,323 mol wt with a signal peptide, a membrane anchor sequence, a large external domain containing potential N-glycosylation sites, and a charged C- terminal cytoplasmic domain. We suppose that this amino acid sequence corresponds to gH of HSV-1, and A. Davison (personal communication) has noted the existence of homologous glycoproteins predicted from the nucleotide sequences of Varicella-zoster virus and Epstein-Barr virus. The properties of monoclonal antibody LP11, directed against gH show remarkable similarities to the properties for gD antibodies. LP11 efficiently neutralizes virus infectivity, blocks cell fusion by syncytial virus strains, and inhibits the formation of plaques when added to cell monolayers after infection. These similarities in antibody activity imply functional relatedness between gH and gD of herpes simplex virus.

Characterization of the genes encoding herpes simplex virus type 1 and type 2 alkaline exonucleases and overlapping proteins

A detailed sequence analysis of the herpes simplex virus type 1 (HSV-1) and HSV-2 DNA encoding the alkaline exonuclease mRNA clusters has been completed. Three partially colinear mRNAs (2.3, 1.9, and 0.9 kilobases) are completely encoded within the DNA sequence presented. The putative promoter regions of the transcripts were inserted upstream of a plasmid-borne chloramphenicol acetyl transferase (CAT) gene and assayed for their ability to induce transcription of the CAT gene upon low multiplicity of infection with HSV in transient expression assays. We conclude that the expression of all three transcripts appear to be controlled by individual promoters. The 2.3-kilobase mRNA contains an open translational reading frame sufficient to encode 626 amino acids for the HSV-1 alkaline exonuclease enzyme; this value is 620 amino acids for HSV-2. A comparison of the predicted amino acid sequences of the HSV-1 and HSV-2 alkaline exonuclease enzymes revealed significant amino acid differences in the N-terminal portions of the two proteins; however, computer analyses suggest that the three-dimensional structures of the HSV-1 and HSV-2 nuclease enzymes are very similar. The 0.9-kilobase mRNA contains an open reading frame which shares a small amount of out-of-phase overlap with the C-terminal portion of the alkaline nuclease open reading frame. This open reading frame has the capacity to encode a 96-amino-acid polypeptide (10,500 daltons).

Transcriptional control of herpesvirus gene expression: gene functions required for positive and negative regulation

We have used an in vitro nuclear run-off assay to measure the levels of transcription of specific herpes simplex virus genes at different times during a lytic infection. We analyzed the effects of inhibition of DNA replication and of defects in two herpes simplex virus regulatory proteins on the transcription of these genes. We present evidence that the transcription of the alpha ICP4 gene is negatively regulated during a lytic infection. The regulation of ICP4 gene transcription requires the beta protein ICP8 (where ICP = infected cell polypeptide). Transcription of the beta ICP8, gamma 1 ICP5, and gamma 2 glycoprotein C (gC) genes was dependent on ICP4, and transcription of the gamma 2gC gene was strongly inhibited when DNA replication was blocked. Defects in ICP8 also resulted in increased levels of transcription of the ICP4, ICP8, ICP5, and gC genes from parental viral genomes. Our results suggest that ICP8 may be important in maintaining the highly ordered cascade of viral gene expression.

Virus-induced modification of the host cell is required for expression of the bacterial chloramphenicol acetyltransferase gene controlled by a late herpes simplex virus promoter (VP5)

The requirements for expression of genes under the control of early (alkaline exonuclease) and late (VP5) herpes simplex virus type 1 (HSV-1) gene promoters were examined in a transient expression assay, using the bacterial chloramphenicol acetyltransferase gene as an expression marker. Both promoters were induced, resulting in the production of high levels of the enzyme upon low-multiplicity infection by HSV-1. S1 nuclease analysis of hybrids between RNA isolated from infected cells containing HSV-1 promoter constructs and marker gene DNA demonstrated normal transcriptional initiation of the marker gene directed by the viral promoters. Viral DNA sequences no more than 125 bases 5' of the putative transcriptional cap site were sufficient for maximum activity of the late promoter. In contrast to expression controlled by the early gene, the late promoter was not active at a measurable level in uninfected cells until DNA sequences between 75 and 125 bases 5' of the transcriptional cap site were deleted. Cotransfection of cells with the expression marker controlled by HSV promoters and a cosmid containing HSV alpha (immediate-early) genes indicated that full expression of both early and late promoters requires the same virus-induced host cell modifications. Inhibition of viral DNA synthesis results in an increased rate of transient expression of marker genes under control of either early or late promoters in contrast to the situation in normal virus infection. These data provide evidence that the normal course of expression of late HSV genes involves negative modulation of potentially active promoters in the infected cell.

An unusual spliced herpes simplex virus type 1 transcript with sequence homology to Epstein-Barr virus DNA

High-resolution transcription mapping localized a spliced 2.7-kilobase herpes simplex virus type 1 mRNA. The 4-kilobase intron of this transcript encodes a nested set of transcripts on the opposite DNA strand. The nucleotide sequence of the DNA encoding the left-hand and right-hand exons of the spliced transcript was determined, and the salient features are presented here. Of major interest is that both exons contained regions within several hundred bases of the splice donor and acceptor sites which showed homology to two regions of the Epstein-Barr virus genome, which are themselves 3 kilobases apart. The spliced herpes simplex virus transcript encoded a translational reading frame which could encode a protein with an approximate size of 75,000 daltons. This value is in agreement with in vitro translation data. The predicted amino acid sequence of the herpes simplex virus protein had significant homology with putative amino acid sequences encoded by the homologous Epstein-Barr virus DNA sequences.

Accumulation of herpes simplex virus type 1 RNAs of different kinetic classes in the cytoplasm of infected cells

We have analyzed the accumulation of herpes simplex virus type 1 RNA of the immediate early (IE; infected cell polypeptide types 4 and 0 [ICP-4 and ICP-0]), early (thymidine kinase), and early late (ICP-5) kinetic classes in the cytoplasm of infected cells in the presence of anisomycin, canavanine, or phosphonoacetic acid and in the course of a normal infection. IE RNAs were overproduced and were the only class of transcript detected in anisomycin-blocked cells. Phosphonoacetic acid treatment resulted in overaccumulation of early RNAs and underaccumulation of early late RNAs. Although low-stringency canavanine treatment resulted in accumulation of RNA from all kinetic classes, high-stringency conditions restricted accumulation of herpes simplex virus type 1 RNAs to the IE class. More importantly, the IE RNAs for ICP-4 and ICP-0 accumulated to a lesser extent under high-stringency canavanine conditions compared with their accumulation in anisomycin-treated cells. Therefore, the absence of newly synthesized viral proteins (anisomysin treatment) and the presence of analog proteins (stringent canavanine treatment) have different consequences with regard to the accumulation of these two IE RNAs. The kinetics of cytoplasmic accumulation for these RNAs was different for each class of RNA. The IE RNAs were detectable at 1 h postinfection and reached a maximum accumulation at ca. 3 h postinfection. The IE RNAs for both ICP-4 and ICP-0 persisted at late times of infection; however, they differed in that the RNA for ICP-4 remained at relatively low levels and the RNA for ICP-0 remained at relatively high levels as compared with their peak levels of accumulation. The 1.4-kilobase RNA for the herpes simplex virus type 1 thymidine kinase was detected by 2 h, with maximum accumulation occurring at ca. 5 h postinfection. After the peak of accumulation, the amount of thymidine kinase RNA declined rapidly from 8 to 14 h postinfection. The early late RNA for ICP-5 was detected between 2 and 3 h, after which accumulation increased to a peak between 8 and 10 h postinfection. The level of ICP-5 RNA remained at close to the peak level until 14 h postinfection. We also compared the accumulation of viral mRNAs in the cytoplasm with the rates of synthesis of their respective polypeptides. Our results suggest that translational controls may be involved in the regulation of IE genes but not early or late genes.

Herpes simplex virus types 1 and 2 homology in the region between 0.58 and 0.68 map units

The homology between herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2, respectively) DNA between 0.58 and 0.674 map units was compared by Southern and dot blot analysis with DNA of one type of virus as a hybridization probe against the other type. Regions of high homology were interspersed with regions of detectably lower homology. However, only one region (between 0.647 and 0.653 map units) contained few or no homologous sequences. In situ RNA blot hybridization demonstrated that the mRNA species transcribed in the right-hand portion of the region are homologous between HSV-1 and HSV-2, as was previously found for the left-hand portion. A 2.7-kilobase HSV-2 transcript in the right-hand portion of the studied region was clearly that encoding HSV-2 glycoprotein C. Comparative nucleotide sequence analysis of specific regions demonstrated that homologous translational reading frames could be identified in the virus types. This analysis also demonstrated that homology could be abruptly lost outside such reading frames. Comparison of regions of homology with published HSV-1 transcription maps suggests that there can also be large divergence within translational reading frames. Some, but not complete, sequence homology was seen in the putative promoter sequence for the 730-base HSV-1 mRNA mapping to the right of glycoprotein C and the corresponding HSV-2 DNA. This suggests that the rather strict conservation of promoter sequences between homologous HSV-1 and HSV-2 transcripts seen in other regions of the genome may not be a necessary feature between these virus types.

Molecular basis of the glycoprotein-C-negative phenotype of herpes simplex virus type 1 macroplaque strain

The basis for the inability of the macroplaque (MP) strain of herpes simplex virus type 1 to express mature glycoprotein C (gC) was examined. RNA transfer (Northern) blot analysis with hybridization probes from the region of the herpes simplex virus type 1 DNA known to encode the gC gene indicated that gC mRNA was produced in MP-infected HeLa cells at levels relative to other mRNAs comparable with that seen in KOS-infected cells. Comparative nucleotide sequence analysis of the gC gene from the MP and KOS strains, coupled with the results of recently reported marker rescue experiments, indicates that the inability of MP to produce gC is due to a frameshift mutation in the gC-coding sequence. Because two different (out-of-phase) open reading frames overlap the gC-coding sequence in the region of the mutation, MP mRNA can encode two gC-related polypeptides. Two polypeptides of the predicted size and precipitable by anti-gC antibodies were produced by in vitro translation of MP mRNA. These polypeptides have not been detected in extracts from infected cells with the same antibodies. Comparative nucleotide sequence analyses led to several corrections in the published sequence for the gC gene and the 17,800-molecular-weight polypeptide gene just to the right in KOS DNA. These relatively minor effects on the predicted amino code sequence of gC are tabulated.

Regulation of HSV transcription

Herpes simplex virus (HSV) transcripts share many features with both cellular mRNA and the mRNAs expressed by other nuclear-replicating DNA viruses: they are capped, polyadenylated, and generally have an approximately 150 base leader between the cap and translation initiation codon. Further, certain sequence features around individual transcription units are shared: HSV promoters contain TATA and often CATC boxes, and the sequence signal indicating a polyadenylation site (AATAAAA) is standard. In spite of these similarities, there is one very distinct difference between the structure of HSV transcription units and those of other nuclear replicating DNA viruses. Each HSV transcript appears to be controlled by its own promoter and encodes a specific polypeptide. Further, the high degree of splicing seen with most eukaryotic and viral mRNAs is not seen in HSV. Certainly, HSV and other herpesviruses do express some spliced transcripts, but these are in the minority (with HSV at least). Thus a whole hierarchy of potential control points utilized in eukaryotic gene expression is missing or rarely utilized in HSV. Despite this, the high density of gene packaging and relatively complex arrangement of partially overlapping transcripts is seen in HSV transcription as it is in other, smaller DNA viruses.

Nucleotide sequence specifying the glycoprotein gene, gB, of herpes simplex virus type 1

The nucleotide sequence thought to specify the glycoprotein gene, gB, of the KOS strain of herpes simplex virus type 1 (HSV-1) has been determined. A 3.1-kilobase (kb), viral-specified RNA was mapped to the left half of the BamHI-G fragment (0.345 to 0.399 map units). TATA, CAT-box, and possible mRNA start sequences characteristic of HSV-1 genes are found near 0.368 map units. The first available ATG codon is at 0.366 and the first in-phase chain terminator at 0.348 map units. A polyA-addition signal (AATAAA) occurs 17 nucleotides past the chain terminator. Translation of these sequences would yield a 100.3-kilodalton (kDa) polypeptide characterized by a 5' signal sequence, nine N-linked saccharide addition sites, a strongly hydrophobic membrane-spanning sequence, and a highly charged 3' cytoplasmic anchor sequence. Two mutants of KOS, tsJ12 and tsJ20, that are temperature-sensitive for viral growth and for the production of gB, have been physically mapped to 0.357 to 0.360 and 0.360 to 0.364 map units, respectively (DeLuca et al., in preparation). The nucleotide sequence of the mutants was determined in these regions. In both cases a single amino acid replacement within the 100.3-kDa polypeptide is predicted from the sequence analysis.

Direct demonstration that the abundant 6-kilobase herpes simplex virus type 1 mRNA mapping between 0.23 and 0.27 map units encodes the major capsid protein VP5

The two partially colinear 6-kilobase (kb) and 1.5-kb mRNAs mapping between 0.23 and 0.27 map units on the herpes simplex virus type 1 genome were precisely located. The 5' end of the 6-kb mRNA was located 28 bases downstream of the sequence ATATATT and was 10 bases to the left of the BamHI site at 0.268. This position is ca. 90 bases to the left of our earlier reported sequence (R. J. Frink, K. G. Draper, and E. K. Wagner, Proc. Natl. Acad. Sci. U.S.A. 78:6139-6143, 1981). We used a polyclonal antibody made against purified herpes simplex virus type 1 VP5 to demonstrate that the 155,000-dalton translation product of the 6-kb mRNA is this capsid protein. The antibody did not react with the 35,000-dalton translation product of the 1.5-kb mRNA. We also confirmed our identification of VP5 as the translation product of the 6-kb mRNA by comparison of tryptic peptides of the in vitro-translated protein and authentic VP5.

High-resolution characterization of herpes simplex virus type 1 transcripts encoding alkaline exonuclease and a 50,000-dalton protein tentatively identified as a capsid protein

Four partially overlapping mRNAs (1.9, 2.3, 3.9, and 4.5 kilobases [kb]) were located between 0.16 and 0.19 map units on the herpes simplex virus type 1 genome. Their direction of transcription was found to be from right to left. The 2.3-kb mRNA was found to be early (beta), whereas the others were late (beta gamma). Partial sequence analysis of the DNA encoding these genes indicated that the promoter for the 2.3-kb mRNA shares structural features with other early (beta) promoters. In vitro translation of hybrid-selected mRNA indicated that among the proteins these mRNAs encode are an 82,000-dalton (d) polypeptide reactive with a monoclonal antibody against herpes simplex virus type 2 alkaline exonuclease and a 50,000-d polypeptide weakly reactive with a polyclonal antibody made against the capsid protein VP19C. Further experiments suggested that the 2.3-kb mRNA encodes the 82,000-d polypeptide, whereas one (or both) of the larger mRNAs encodes the 50,000-d protein. A novel finding was that the 1.9-kb mRNA appears to share part of the translational reading frame for alkaline exonuclease, but any polypeptide it encodes does not react with the monoclonal antibody to this enzyme.

Mutations in the major DNA-binding protein gene of herpes simplex virus type 1 result in increased levels of viral gene expression

We have examined the effect of temperature-sensitive mutations in the herpes simplex virus 1 DNA-binding protein gene on viral gene expression. We have found that at the nonpermissive temperature, the synthesis of certain immediate early, early, and late viral polypeptides was greater in cells infected with the temperature-sensitive mutants than in cells infected with the wild-type virus. This effect was independent of the requirement for this viral protein for viral DNA replication. The altered rate of synthesis of viral proteins was due to a thermolabile gene product. Cells infected with these mutants at the permissive temperature and then shifted to the nonpermissive temperature exhibited enhanced levels of viral gene expression. The addition of actinomycin D at the time of the temperature shift prevented the alteration in viral protein synthesis. Therefore, continuing transcription is required for this change in gene expression. Northern blot analysis of cytoplasmic RNA showed that the steady-state level of specific viral transcripts expressed from parental virus genomes was greater in cells infected by these mutants at the nonpermissive temperature. These results indicate that the major DNA-binding protein of herpes simplex virus type 1 acts as a negative regulator of viral gene expression by affecting the abundance of cytoplasmic viral mRNAs.

Detailed analysis of the portion of the herpes simplex virus type 1 genome encoding glycoprotein C

We previously showed that the right third of HindIII fragment L (0.59 to 0.65) of herpes simplex virus type 1 (HSV-1) encodes a family of mRNAs some members of which appear to be related by splicing. In the experiments described in this communication, we determined the nucleotide sequence of the DNA encoding this mRNA family and precisely located the mRNAs associated with this DNA sequence. The major mRNA species is unspliced and encoded by a 2.520-nucleotide region. Just upstream of the 5' end are TATA and CAT box sequences characteristic of HSV-1 promoters. The 3' end maps near a region containing a nominal polyadenylation signal. Three minor species (2,400, 2,200, and 1,900 bases, respectively) appear to share a very short leader sequence with the 5' end of the major mRNA and are then encoded by uninterrupted DNA sequences beginning about 100, 400, and 625 bases downstream of the 5' end of the major unspliced mRNA. These positions map at or very near positions which agree reasonably well with consensus splice acceptor sequences. The fourth mRNA is encoded by a contiguous 730-nucleotide sequence at the 3' end of the major unspliced mRNA and has its 5' end just downstream of recognizable TATA and CAT box sequences. We suggest that this mRNA is controlled by its own promoter. The nucleotide sequence data, in combination with the mRNA localization, demonstrate four potential polypeptides encoded by the region. The largest is 1,569 bases long and defines a 523-amino acid protein with sequence features characteristic of a glycoprotein. This was confirmed to be HSV-1 glycoprotein C by immune precipitation of the in vitro translation product of the major unspliced mRNA, performed with a polyspecific antibody to HSV-1 envelope glycoproteins (anti-env-1 serum), and by comparison of tryptic peptides of this translation product with those of authentic HSV-1 glycoprotein C. Polypeptides encoded by some of the minor species also were tentatively identified.

Transcription of herpes simplex virus genes in vivo: overlap of a late promoter with the 3' end of the early thymidine kinase gene

We identified in herpes simplex virus type 1-infected cells six cytoplasmic transcripts which were complementary to BamHI restriction endonuclease fragment Q. Two transcripts appeared in major amounts compared with the other four. One major transcript of about 1.4 kilobases was the mRNA for the viral thymidine kinase, was synthesized at intermediate times, and was classified as a beta transcript. The other major transcript was synthesized at late times and was classified as a gamma transcript. This late transcript was about 3 kilonucleotides long and was transcribed in the same direction as the gene for thymidine kinase. The 5' end of this late RNA was located by RNA sequence analysis and was 23 nucleotides downstream from the polyadenylation site for the thymidine kinase mRNA. This finding led to the conclusion that the control region for the 3-kilobase gamma transcript is contained within the 3' untranslated region of the thymidine kinase transcript.

Detection by RNA blot hybridization of RNA sequences homologous to the BglII-N fragment of herpes simplex virus type 2 DNA

RNA species, extracted at the time of peak synthesis of the alpha, beta, and gamma classes of herpes simplex virus polypeptides from lytically infected Vero cells, were examined for homology to the BglII-N fragment (map units 0.58 to 0.63) of herpes simplex virus type 2 DNA. By using northern blot analysis, two major and several minor polyadenylated RNA species showed homology to the BglII-N fragment at times corresponding to the maximum synthesis of the beta (7 h postinfection) and gamma (12 h postinfection) herpes simplex virus polypeptides. No alpha RNA homologous to the BglII-N fragment was detected.

Detailed characterization of an apparently unspliced beta herpes simplex virus type 1 gene mapping in the interior of another

We precisely localized the coding region and determined the nucleotide sequence of a 1.2-kilobase beta herpes simplex virus type 1 mRNA which underlies the 3' region of the 5.2-kilobase beta mRNA mapping in HindIII fragment K. This mRNA, which lacks readily detectable splices, has its own promoter by the criteria of identification of putative herpes simplex virus type 1 control sequences and in vitro transcription by a Manley polymerase system.

Herpes simplex virus mRNA species mapping in EcoRI fragment I

We described the detailed characterization and high-resolution mapping of nine herpes simplex virus type 1 mRNAs encoded in EcoRI fragment I. Four of these mRNAs are partially colinear and encode the same sized polypeptide in vitro. Nucleotide sequence analysis of the DNA around the 5' ends of these mRNAs suggested that the larger may encode a small (ca. 100-dalton) polypeptide not resolvable by in vitro translation.

mRNA- and DNA-directed synthesis of herpes simplex virus-coded exonuclease in Xenopus laevis oocytes

Microinjection of herpes simplex virus (HSV)-infected cell mRNA into Xenopus laevis oocytes resulted in the production of a new exonuclease activity. This enzyme strongly resembled the HSV alkaline exonuclease in many biochemical properties, and hybrid-arrested translation studies showed that it was virus coded, mapping at 0.080 to 0.185 genome map units. Exonuclease mRNA had a size and genome location equivalent to the mRNA encoding V185 in reticulocyte lysates, suggesting that V185 is the exonuclease. The enzyme synthesized in oocytes was found to act as an exonuclease in vivo. Two plasmids containing HSV DNA fragments directed the synthesis of exonuclease when microinjected into oocyte nuclei, and this finding enabled the coding and control sequences for this gene to be localized to 0.155 to 0.185 genome map units.

Identification of proteins encoded by a fragment of herpes simplex virus type 2 DNA that has transforming activity

Cloned BglII fragment N (map units 0.58 to 0.625) of herpes simplex virus type 2 DNA has been shown to transform rodent cells to an oncogenic phenotype (Galloway and McDougall, J. Virol. 38: 749-760, 1981). RNA homologous to this fragment directs the synthesis of five polypeptides in a cell-free translation system. The approximate molecular weights of these proteins are 140,000, 61,000, 56,000, 35,000, and 23,500. The 35,000-dalton protein is the major species late in infection and is the only species detected before the onset of viral DNA replication. The arrangement of the sequences encoding these proteins along the herpes simplex virus type 2 genome was determined by hybridization of the RNA to cloned PstI fragment of BglII-N and to single-stranded DNA segments cloned into M13mp7. Both the hybridization experiments and immunoprecipitation with monoclonal antibodies suggested that the 140,000- and 35,000-dalton proteins are at least partially colinear and share antigenic determinants.

Detailed structural analysis of two spliced HSV-1 immediate-early mRNAs

The structures of two HSV-1 immediate-early mRNAs have been determined by nuclease-digestion procedures using 5' and 3' end-labelled DNA probes. These mRNAs, which map across the junctions between the short unique (US) and short repeat (IRS and TRS) genome regions, have common 5' portions located in IRS and TRS. The 3' portions, which extend into opposite ends of US, and unique. The DNA sequence encoding the common 5' portions largely comprises a 247 base pair (bp) leader region and a single intron of variable size. The variation in intron length is due to different copy numbers of a 22 bp tandem reiteration. A small proportion of the mRNA population is unspliced, but otherwise is identical to the more abundant spliced species.

The immediate-early mRNA that encodes the regulatory polypeptide Vmw 175 of herpes simplex virus type 1 is unspliced

The structure and precise map location of the 4.1-kb herpes simplex virus type 1 (HSV-1) immediate-early mRNA (IE mRNA-3) that encodes a regulatory polypeptide, with an approximate mol. wt. of 175 000, has been determined. Nuclease S1 digestion procedures using labelled virus DNA probes have shown that IE mRNA-3 is unspliced and maps entirely within the TRs/IRs genome regions. DNA sequences at the 5' and 3' ends of IE mRNA-3 have been examined and regulatory signals involved in initiation of transcription and polyadenylation have been identified. No other mRNA is known to map within the region coding for IE mRNA-3.

Uninfected cell polymerase efficiently transcribes early but not late herpes simplex virus type 1 mRNA

The sequences of the DNAs encoding the 5' ends of one early and one late herpes simplex virus type 1 mRNA were analyzed, and the 5' ends of these mRNA species were precisely located. Neither mRNA species is spliced and the noncoding strand of the DNA contains recognizable T-A-T-A and C-A-T boxes upstream from their respective 5' ends. The early mRNA was efficiently transcribed by a commercially available uninfected cell lysate system, but the late mRNA was not. This difference between early and late mRNAs appears to be general in this virus.

Herpes simplex virus type 1 HindIII fragment L encodes spliced and complementary mRNA species

We have used DNA bound to cellulose to isolate and translate in vitro herpes simplex virus type 1 (HSV-1) mRNA's encoded by HindIII fragment L (mapping between 0.592 and 0.647), and 8.450-base-pair (8.45-kb) portion of the long unique region of the viral genome. Readily detectable, late mRNA's 2.7 and 1.9 kb in size encoding 69,000- and 58,000-dalton polypeptides, respectively, were isolated. A very minor late mRNA family composed of two colinear forms, one 2.6 kb and one 2.8 kb, was isolated and found to encode only an 85,000-dalton polypeptide. A major early mRNA, 1.8 kb in size encoding a 64,000-dalton polypeptide, was also isolated. High-resolution mapping of these mRNA's by using S1 nuclease and exonuclease VII digestion of hybrids between them and 5' and 3' end-labeled DNA fragments from the region indicated that the major early mRNA contained no detectable splices, and about half of its 3' end was complementary to the 3' region of the very minor 2.6- to 2.8-kb mRNA's encoded on the opposite strand. These mRNA's also contained no detectable splices. The major late 2.7-kb mRNA was found to be a family made up of members with no detectable splices and members with variable-length (100 to 300 bases) segments spliced out very near (ca. 50 to 100 bases) the 5' end.